During knitting operation of a conventional circular knitting machine, if there is a need to do jacquard knitting of different colors on the fabric, a color altering head is installed on a yarn feeding bore of the circular knitting machine. The color altering head can move a color yarn to the yarn feeding bore to be picked up by a knitting needle so that the colored yarn is knitted into the fabric to achieve jacquard knitting effect that contains different colors.
Refer to FIGS. 1A through 1D for a fragmentary structure of a conventional single-face color altering head in operations. The single-face color altering head mechanism 1 includes a yarn feeding plate 11, a yarn clipping plate 12 and a spacer 13. The yarn feeding plate 11 has a butt 112 driven by a cam (not shown in the drawings) of the circular knitting machine to push the yarn feeding plate 11 forwards (referring to FIG. 1A). A colored yarn threading through a yarn feeding eye 116 is picked up by the yarn clipping plate 12 and clipped between the yarn clipping plate 12 and the spacer 13, and can be drawn (not shown in the drawings). While the yarn feeding plate 11 is moved and a thrust portion 114 of the yarn feeding plate 11 is in contact with a thrust lug 122 of the yarn clipping plate 12, the yarn clipping plate 12 is driven forwards by the yarn feeding plate 11 (referring to FIG. 1B). Then the color yarn clipped between the yarn clipping plate 12 and the spacer 13 is released to be knitted by the knitting needle of the circular knitting machine. When the needle selection device (not shown in the drawings) of the circular knitting machine changes another colored yarn, another set of yarn feeding plate and yarn clipping plate (not shown in the drawings) operate as previously discussed to pick up and release another color yarn for knitting operation. Meanwhile, the yarn feeding plate 11 is immediately driven by the cam (not shown in the drawings) to retract the yarn feeding plate 11 through a drawing portion 113 formed thereon (referring to FIG. 1C), and the colored yarn threading through the yarn feeding eye 116 is picked up by the yarn feeding plate 11, and the yarn is moved along the path of an action slot 111 to be transversely saddled on a yarn clipping portion 121 (not shown in the drawings) of the yarn clipping plate 12. When the yarn feeding plate 11 is moved and a retracting portion 115 thereof is in contact with a retracting lug 123 of the yarn clipping plate 12, the yarn clipping plate 12 is retracted by a reward driven force of the yarn feeding plate 11 (referring to FIG. 1D). As the color yarn is transversely saddled on the clipping portion 121 (not shown in the drawings), the yarn clipping plate 12 is moved rewards to the spacer 13 by the yarn feeding plate 11, and a shearing force is generated to sever the colored yarn and clip the colored yarn between the yarn clipping plate 12 and the spacer 13. Thereby different colored yarns can be changed in the knitting operation, and the resulting knitted fabric has colorful jacquard effect.
However, the conventional color altering head previously discussed mainly aims to be used in the circular knitting machine operating at a regular speed to place the altered yarn transversely on the clipping portion 121, and generate a shearing force with the spacer 13 to sever the yarn, and clip the yarn between the yarn clipping plate 12 and the spacer 13. When the conventional color altering head is used at high speed (about 25 RPM), two serious problems occur: 1. During operation of the yarn feeding plate 11, an extra action of driving the yarn clipping plate 12 is needed. Hence operation cycle is longer, and high speed knitting operation is hindered. Moreover, the constant driving of the yarn clipping plate 12 and the associated hitting generate metal impact and bouncing. This also impairs high speed operation. 2. As the yarn clipping plate 12 is driven by the yarn feeding plate 11 at a selected operation speed, the color altering head also has to be designed and function at the selected operation speed. In the event that the circular knitting machine runs at an operation speed higher than the designed level, the yarn cannot be straddled on the clipping portion 121 or the clipping portion 121 cannot clip the severed yarn, yarn dropping occurs.